[PATCH v3] PCI: Fix crash during pci_dev hot-unplug on pseries KVM guest

[Amit Machhiwal]

Hi Michael,

On 2024/08/17 08:59 AM, Michael Ellerman wrote:
> Amit Machhiwal <amachhiw at linux.ibm.com> writes:
> > On 2024/08/15 01:20 PM, Michael Ellerman wrote:
> >> Bjorn Helgaas <helgaas at kernel.org> writes:
> >> > On Sat, Aug 03, 2024 at 12:03:25AM +0530, Amit Machhiwal wrote:
> >> >> With CONFIG_PCI_DYNAMIC_OF_NODES [1], a hot-plug and hot-unplug sequence
> >> >> of a PCI device attached to a PCI-bridge causes following kernel Oops on
> >> >> a pseries KVM guest:
> >> >
> >> > What is unique about pseries here?  There's nothing specific to
> >> > pseries in the patch, so I would expect this to be a generic problem
> >> > on any arch.
> >> >
> >> >>  RTAS: event: 2, Type: Hotplug Event (229), Severity: 1
> >> >>  Kernel attempted to read user page (10ec00000048) - exploit attempt? (uid: 0)
> >> >>  BUG: Unable to handle kernel data access on read at 0x10ec00000048
> >> >
> >> > Weird address.  I would expect NULL or something.  Where did this
> >> > non-NULL pointer come from?
> >> 
> >> It originally comes from np->data, which is supposed to be an
> >> of_changeset.
> >> 
> >> The powerpc code also uses np->data for the struct pci_dn pointer, see
> >> pci_add_device_node_info().
> >> 
> >> I wonder if that's why it's non-NULL?
> >
> > I'm also looking into the code to figure out where's that value coming from. I
> > will update as soon as I get there.
> 
> Thanks.
>  
> >> Amit, do we have exact steps to reproduce this? I poked around a bit but
> >> couldn't get it to trigger.
> >
> > Sure, below are the steps:
> >
> > 1. Set CONFIG_PCI_DYNAMIC_OF_NODES=y in the kernel config and compile (Fedora
> >    has it disabled in it's distro config, Ubuntu has it enabled but will have it
> >    disabled in the next update)
> >
> > 2. If you are using Fedora cloud images, make sure you've these packages
> >    installed:
> >     $ rpm -qa | grep -e 'ppc64-diag\|powerpc-utils'
> >     powerpc-utils-core-1.3.11-6.fc40.ppc64le
> >     powerpc-utils-1.3.11-6.fc40.ppc64le
> >     ppc64-diag-rtas-2.7.9-6.fc40.ppc64le
> >     ppc64-diag-2.7.9-6.fc40.ppc64le
> >
> > 3. Hotplug a pci device as follows:
> >     virsh attach-interface <domain_name> bridge --source virbr0
> 
> I don't use virsh :)

No worries. Fortunately, we do have a way to do it with qemu monitor.

> 
> Any idea how to do it with just qemu monitor commands?
> 

1. Boot the guest with the below included in the qemu cmdline:

    -netdev bridge,id=<net_name>,br=virbr0,helper=/usr/libexec/qemu-bridge-helper

2. Once the guest boots, run the below command on qemu monitor to hot-plug a pci
   device:

    device_add rtl8139,netdev=<net_name>,mac=52:54:00:88:31:28,id=<net_id>

    dmesg
    =====
    [  116.968210] pci 0000:00:01.0: [10ec:8139] type 00 class 0x020000 conventional PCI endpoint
    [  116.969260] pci 0000:00:01.0: BAR 0 [io  0x10000-0x100ff]
    [  116.969904] pci 0000:00:01.0: BAR 1 [mem 0x00000000-0x000000ff]
    [  116.970745] pci 0000:00:01.0: ROM [mem 0x00000000-0x0003ffff pref]
    [  116.971456] pci 0000:00:01.0: No hypervisor support for SR-IOV on this device, IOV BARs disabled.
    [  116.972583] pci 0000:00:01.0: Adding to iommu group 0
    [  116.978466] pci 0000:00:01.0: ROM [mem 0x200080080000-0x2000800bffff pref]: assigned
    [  116.979347] pci 0000:00:01.0: BAR 0 [io  0x10400-0x104ff]: assigned
    [  116.980063] pci 0000:00:01.0: BAR 1 [mem 0x200080001000-0x2000800010ff]: assigned
    [  117.017187] 8139cp: 8139cp: 10/100 PCI Ethernet driver v1.3 (Mar 22, 2004)
    [  117.018577] 8139cp 0000:00:01.0: enabling device (0000 -> 0003)
    [  117.025414] 8139cp 0000:00:01.0 eth1: RTL-8139C+ at 0x00000000fbf09e59, 52:54:00:88:31:28, IRQ 26
    [  117.051028] 8139too: 8139too Fast Ethernet driver 0.9.28
    [  117.076577] 8139cp 0000:00:01.0 eth1: link up, 100Mbps, full-duplex, lpa 0x05E1

3. Try hot-unplug of the device to recreate the kernel Oops.

    device_del <net_id>

Thanks,
Amit

> cheers